The widespread growing popularity of the Internet has encouraged wireless communication system developers to continually improve the data communication capabilities of their systems. In response to this need, various standards bodies are formulating new third generation (3G) standards which support higher data rates. For example, standards organizations such as the European Telecommunications Standards Institute (ETSI), the Association of Radio Industries and Broadcasting (ARIB) and the Telecommunications Industry Association (TIA) are continually working to develop standards to support faster and more efficient wireless communications.
Consequently, the wireless communications industry is developing and implementing new wireless transmission protocols, which provide faster, more robust and more efficient data communications over an air interface. For example, general packet radio service (GPRS) has been developed as a packet-switched upgrade for the well known time division multiple access (TDMA) system. In a further advancement in the art, enhanced GPRS (EGPRS) has also been developed.
In wireless packet data systems such as Enhanced General Packet Radio Service (EGPRS), selective automatic repeat request (ARQ) is used for error recovery over the radio link. Currently, nine Modulation and Coding Schemes (MCSs) have been proposed for EGPRS with MCS-1 being the most robust and MCS-9 being the least robust scheme. The Radio Link Control (RLC) layer allows full recovery (i.e, there is no limit on the maximum number of retransmissions) and delivers data in-sequence to the higher layer. It does not guarantee a delivery rate or a maximum delivery delay. This scheme is best suited to the support of best effort data services over wireless links, and not to applications such as streaming.
For voice services, the loss and delay requirements are typically very stringent and do not allow sufficient time for any error recovery. Furthermore, with the advances in speech coding, the rates demanded by voice services are quite low (<12–16 kb/s). Therefore, the typical approach is to transmit enough redundant information to allow operation under poor channel conditions. The channel coding is fixed and no retransmissions are allowed. This approach is also not well suited to streaming services since the delay requirements for streaming are typically more relaxed than packet voice. As a result, it is not necessary to limit the achievable efficiency by using a fixed amount of redundancy, independent of the actual delay requirements and the prevailing channel quality. Higher streaming rates can be supported if error recovery is carried out using a selective ARQ process with limited retransmission capability.
A streaming service places the following requirements on the radio link control (RLC) protocol: play out rate (R) at receiver RLC; maximum delivery delay (D) where the delivery delay is defined as the time between arrival of data at the transmitter RLC and play out by the receiver RLC to the higher layer; and maximum residual loss rate, L. EGPRS R1999 Radio Link Control (RLC) block segmentation and retransmission procedures have already been specified by ETSI GSM 04.60 R1999, entitled “General Packet Radio Service (GPRS); Mobile Station—Base Station Interface; Radio Link Control/Medium Access Control (RLC/MAC) protocol”; in order to allow: dynamic link adaptation between nine different coding and modulation schemes (MCS-1 to MCS-9) to achieve the best delay/throughput tradeoff under prevailing channel conditions; and incremental Redundancy (IR) operation where the amount of redundant information sent with the initial transmission or subsequent retransmissions of an RLC block depends on the prevailing MCS. ETSI GSM 04.60 R1999, entitled “General Packet Radio Service (GPRS); Mobile Station—Base Station Interface; Radio Link Control/Medium Access Control (RLC/MAC) protocol.” is hereby incorporated by reference. Also, EGPRS R1999 Radio Link Control specification is incorporated by reference.
EGPRS R1999 does not support streaming services efficiently and it is difficult for it to provide the streaming requirements described above. It is desirable to provide a method and apparatus for radio link control that satisfies the above streaming requirements.